In many fields of engineering, it is conventional practice to determine certain quantities, values or positions by means of closed or open loop control. This is accomplished by utilizing a regulator to deliver a quantity, usually electrical, indicative of a specific function course to some final controlling element; the regulator processes specific input signals from the controlled system and also includes in its control action the result obtained by the adjustment of the final controlling element. If, in the overall configuration of an open or closed loop control, disturbances or other undesired influencing quantities result which are exclusively attributable to the action of the final controlling element, in other words, the characteristic of the final controlling element does not follow exclusively the desired value supplied to it, then substantial deviations from the set values may occur which may give rise to overshoot depending on the time constants occurring, or the control may be too slow.
While being generally suitable for the adaptation of the characteristic of any kind of final controlling element, the invention will be explained in the following with reference to a preferred embodiment, applied to the action of the final controlling element in the idle air charge controller for an internal combustion engine, since this is a preferred field of application for the invention.
Thus, it is known to regulate the idle speed of an internal combustion engine such that an idle speed regulator receives specific data on the instantaneous operating condition of the internal combustion engine including, for example, intake manifold pressure, instantaneous speed, desired idling speed and other peripheral operating data such as throttle position, the position of a bypass valve on which the idle air charge controller especially acts, and/or data on the quantity of intake air or air mass in lieu of the intake manifold pressure.
The idle speed regulator is in a position to determine from these quantities an electrical correcting quantity as a desired value, for example, a signal Q.sub.des indicative of the desired air quantity or a signal m.sub.des indicative of the desired air mass and feed this signal to an idle control element which converts, for example, the air mass desired value into a cross-sectional area of aperture (of the bypass valve referred to above).
It is particularly in the idle air charge controller for an internal combustion engine that allowance has to be made for special conditions such as minimum possible fuel consumption and the keeping constant of a minimum idle speed even on abrupt load changes. Accordingly, idle speed regulators are known (German published patent application DE-OS No. 3,039,435) which are configured to compensate for deviations from a desired speed and to hold such deviations to a low value. However, a problem to be realized in this connection is that speed variations ultimately reflect reactions of the internal combustion engine to external influences and that corresponding speed signals constitute the last link in the control chain, so that necessarily a certain amount of time will elapse between an action on the internal combustion engine and its ensuing reaction thereto. Therefore, in internal combustion engines running at extremely low rpm while idling, there exists at least the danger of an uneven running condition occurring and finally the possibility of a stalled engine if loads with high power requirements such as air conditioners and the like are switched in rapidly.
This problem is even increased by the action of the idle control element itself since the control element characteristic shows a considerable dependency upon the relevant temperature and the operating voltage supplied by the internal combustion engine which likewise may be subject to major variations. Conventionally, idle control elements operate as electromagnetic converters with respect to the adjustment of the cross-sectional area of the aperture through which the internal combustion engine receives the required quantity of air, in which case they may be configured as single-winding controllers or as a magnet part in the actuation of a valve.
With the idle control element cold, the winding of the control element will take up a larger amount of current at a given pulse duty factor; the result is a larger deflection and a corresponding mismatch. Similar negative effects result when the battery voltage varies substantially as is frequently the case in internal combustion engines. Therefore, in order to minimize the mismatch in the control element range, the idle control element requires a complex configuration and a highly consistent characteristic in order to properly convert the electrical actuating quantity supplied to its input into the cross-sectional area of the opening.
However, even with an idle control element reacting as perfectly as possible, unavoidable dependencies remain, such as leakage air flowing past the throttle valve in the idle position, a dependence on altitude of the cross-sectional area of the aperture provided by the idle control element and the like.